Environmental toxins are synthetic contaminants, such as industrial pollutants, and other artificially made, difficult to degradate chemical substances. Multiple chemical compounds are present in our indoor and outdoor air, food, and water. The role of environmental toxins in health has been largely ignored by medicine. Luckily, scientists and practitioners are starting to recognize its importance in health. Currently, many synthetic chemicals are found in human body. In this case we are talking about xenobiotics, a chemical found in an organism but which is not normally produced or expected to be present in it. It can also cover substances which are present in much higher concentrations than are usual. They can harm our health by disrupting sensitive immune, neurological, and endocrine systems, and thus leading to a variety of metabolic and systemic dysfunctions. Several diseases and disorders thought to be environmentally triggered include autism, diabetes, obesity, heart disease, hypertension, stroke, cancer, Alzheimer ’s and Parkinson’s disease (Barbosa et al., 2001; Goldman, 2014; Wang et al., 2011).
In 1983, the World Health Organization (WHO, 1983) introduced the term sick building syndrome (SBS) (Rogers et al., 1987; Godish et al., 1995), and three years later the concept of idiopathic environmental intolerance (Cullen et al., 1987; Hileman et al., 1991; Rea et al., 1992; IPCS / WHO, 1996). This term is sometimes replaced by another name: multiple chemical sensitivity (MCS), which states for hypersensitivity to various chemical stimuli, the source of which are usually synthetic substances. MCS manifests itself in various somatic symptoms that appear in response to low doses of environmental factors. The reality of these ailments is not believed by many doctors, and the status of this disease has remained controversial for many years. Sometimes they are classified as pseudomedical diagnoses, and the nocebo effect (negative beliefs about the state of your health leading to physical disease symptoms) was indicated as a risk factor. However, MCS is not a psychosomatic illness but an overwhelmed hypersensitivity of sensory receptors together with chronic inflammation and a break-up of the body's redox system (Rea, 1996; Pall, 2007; Pall et al., 2009). The problem is also difficult to downplay in the context of the growing number of people suffering from idiopathic diseases.
TYPES OF CHEMICALS AND ROUTES OF ENTRY
There is no single classification applicable for the entire spectrum of xenobiotics; therefore, toxic chemicals are classified in number of ways depending on the interests and needs of the classifier. Classification takes into account both the chemical and biological properties of the agent and exposure characteristics and it’s made based on: (1) sources of toxicants; (2) physical state of toxicants (gaseous toxicants, liquid toxicants, solid toxicants, dust toxicants); (3) target organ/system (neurotoxicants, hepatotoxicants, nephrotoxicants, pulmotoxicants, hematotoxicants, dermatotoxicants); (4) chemical nature/structure of toxicants (metals, nonmetals, acids, and alkalies); (5) organic toxicants; (6) analytical behavior of toxicants (volatile toxicants, extractive toxicants, metals, and metalloids); (7) type of toxicity (acute, subacute, chronic, etc.); (8) toxic effects (carcinogens, mutagens, teratogens, clastogens); (9) usage (insecticides, fungicides, herbicides, food additives, etc.); (10) mechanism of action; or (11) environmental and public health considerations. There are few primary routes of entry into the body: ingestion, skin or eye absorption, inhalation and injection.
WHAT ARE THE MAIN SOURCES OF ENVIRONMENTAL TOXINS?
Human-made chemicals are produced in large scale and are in use all around us. Between 1930 and 2000 global production of synthetic chemicals increased from 1 million to 400 million tonnes each year (WWF, 2019). The U.S. Centers for Disease Control and Prevention (CDC) began measuring human exposure to chemicals in 1976. Up to 300 man-made synthetics have been found in human body, including dichlorodiphenyltrichloroethane (DDT), bisphenol A (BPA), air pollutants, pesticides, dioxins and phthalates. This article is focusing only on few groups of xenobiotics and their impact on selected clinical conditions.
1. PESTICIDES
One of the biggest groups of environmental pollutants are pesticides. Around 2.5 million tons of those chemicals are used worldwide each year: 40% contributed to herbicides, 17% to insecticides, and 10% to fungicides. Pesticide use raises a number of environmental concerns. More than 98% of sprayed pesticides reach a destination other than their target point, and will persists for years as an air, water, and soil pollutants, e.g. chlorinated pesticides which accumulate in the soil persist for decades (Ware et al., 1978) and can easily be brought from the soil into the house, where they contaminate the home as house dust (Raloff, 1996). Growing world population requites more food supplies which results is increasing use of pesticides for crop protection. While pesticides increase agricultural production, bioaccumulation through the food chain become a risk to mammals due to certain negative effects. Moreover, pesticide compounds may be trapped also in human body. The presence of multiple chlorinated hydrocarbons has been found already in 1970s in the adipose tissue (Jensen and Clausen, 1979), and numerous studies from several countries have shown persistent pesticide residues in breast milk (reviewed in Salama, 2017).
2. PLASTIC ADDITIVES
Plastic additives, like phthalates, bisphenol A (BPA) or polybrominated diphenyl ethers (PBDEs), are chemical compounds that are commonly added to plastics to increase their flexibility, transparency, durability and longevity. Phthalates are used in a wide range of cosmetic, household, medical, food products, toys and polyvinyl chloride (PVC) plastic. Diet is believed to be the main source of phthalates because food is commonly packaged or stored in plastics containing this dangerous toxin. On average, people who are eating food prepared outside of the home have nearly 35% higher levels of phthalates circulating in their bodies (Varshavsky et al., 2018). BPA is a carbon-based, synthetic compound that is present in modern-day life. It’s used in everything from plastic water bottles and food storage containers to cash register receipts and canned food and drink liners. Dietary intake is believed to be the biggest exposure point in adults (Chen et al., 2016). Eleven industry-funded studies found that BPA had no effects on health (vom Saal and Welshons, 2006). However, more than 100 independent studies have shown it to be harmful (vom Saal and Welshons, 2006).
3. OUTDOOR AIR POLLUTION
Human activities may be a sources of outdoor air pollution. Those include fuel combustion from motor vehicles, heat and power generation (e.g. oil and coal power plants), industrial facilities (e.g. manufacturing factories, mines, and oil refineries), municipal and agricultural waste sites and waste burning, as well as residential cooking, heating, and lighting with polluting fuels. The pollutants with the strongest adverse health effects include particulate matter (PM), ozone (O3), nitrogen dioxide (NO2) and sulphur dioxide (SO2). PM are inhalable and respirable particles which consist of sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water. Particles smaller that 10 microns (PM10), including fine particles less than 2.5 microns (PM2.5) have the greatest risks to health, as they are capable of penetrating the lungs and entering the bloodstream.
4. INDOOR AIR POLLUTION
Environmental toxins are also found in indoor air and have their origin in a new construction materials or additives that are used to improve the environment at work or home, e.g., wallpaper, varnish and paint. In addition, they are found in textiles such as carpets or clothing. These toxins are regarded as the major causes of what is known as sick building syndrome (SBS), a human diseases resulting from poor indoor air quality due to improper exhaust ventilation or lack of fresh-air intake. Because people in developed countries spend more than 90% of their time indoor, it influences their chemical exposures and, ultimately, health. The average home contains dozens of synthetic chemicals that emits volatile organic compound (VOC). Researchers concluded that trace amounts of highly toxic chemicals are universally present in the dust that builds up in our homes (Mitro et al., 2016). Consequently, chemicals such as phthalates, phenols, flame retardants, and polyfluorinated alkyl substances are widely detected in the population, including pregnant women and children (Woodruff et al., 2011; Mitro et al., 2015). Moreover, indoor use of pesticides, paints, cleaning products, and air fresheners (including candles and incense) distribute toxins throughout the home. In the developing world household air pollution is one of the leading causes of disease and premature death. Exposure to smoke from cooking fires causes 3.8 million deaths each year (WHO, 1983). People in low- and middle-income countries lack the resources to obtain cleaner fuels and devices. Burning fuels such as dung, wood and coal produces a variety of health-damaging pollutants, including PM, methane, carbon monoxide, polyaromatic hydrocarbons and VOC.
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